CARLSBAD, N.M. (AP), For 15 years the trucks have barreled past southeastern New Mexico's potash mines and seemingly endless fields of oil rigs, hauling decades worth of plutonium-contaminated waste to what is supposed to be a safe and final resting place a half mile underground in the salt beds of the Permian Basin.

But back-to-back accidents and a never-supposed-to-happen above-ground radiation release have shuttered the federal government's only deep underground nuclear waste dump indefinitely, raising questions about a cornerstone of the Department of Energy's $5-billion-a-year program for cleaning up legacy waste scattered across the country from decades of nuclear bomb making.

It also highlights a lack of alternatives for disposing of tainted materials like tools, gloves, glasses and protective suits from national labs in Idaho, Illinois, South Carolina and New Mexico.

With operations at the Waste Isolation Pilot Plant on hold, so are all shipments, including the last of nearly 4,000 barrels of toxic waste that Los Alamos National Laboratories has been ordered to remove from its campus by the end of June. The presence of that waste, some of which was dug up from decades-old, unsealed dumps in the northern New Mexico mountains and is now stored outside with little protection, came to the public's attention three years ago as a massive wildfire lapped at the edges of the sprawling lab property.

Sen. Tom Udall, D-N.M., says getting the rest of the waste off the mesa before wildfire season begins is ``paramount,'' but that it is too soon to know if a temporary alternative site for storing the waste needs to be found.

Also on hold are tests to see if the dump can expand its mission to take more than so-called lower level transuranic waste from the nation's research facilities, including hopes by DOE that it can ship hotter, liquid waste from leaking tanks at Washington state's Hanford nuclear waste site.

New Mexico Environment Secretary Ryan Flynn said the state will be looking closely at what caused the leak that exposed at least 13 workers and sent radiation into the air around the plant before deciding whether to back plans to allow the repository to bring in waste from new sources.

``Events like this should never occur,'' he said at a news conference last week where officials confirmed the leak. ``From the state's perspective, one event is far too many.''

Government officials, politicians, the contractors that run the mine and local officials all say it is too soon to speculate on what the short- or long-term impacts of the of the shutdown might be, or where else the toxic waste would go. And they emphasize that all the safety systems designed to react to worst-case scenarios like a ceiling collapse or forklift puncturing one of the huge waste canisters worked.

``A lot of people are just jumping up and down and wanting us to shut down,'' said Farok Sharif, president of the Nuclear Waste Partnership that runs WIPP. ``But that's not the case here. We've designed this facility to look at these types of accidents and we've planned on making sure that we continue to protect our employees and we protect the environment. And our system worked as designed.''

Still, no one yet knows what caused the first-known radiation release from the massive rooms that have been dug out of the 2,000-foot thick ancient Permian Sea bed. Eventually, they will be covered in concrete, with the intent of safely sealing the casks of mostly solid waste 2,150 feet underground and preventing any future release into the environment.

But watchdog Don Hancock of the Southwest Research and Information Center says WIPP has now failed in its long-stated mission ``to start clean, stay clean.''

On Feb. 5, the mine was shut and six workers sent to the hospital for treatment of smoke inhalation after a truck hauling salt caught fire. Nine days later, a radiation alert activated in the area where newly arrived waste was being stored. Preliminary tests show 13 workers suffered some radiation exposure, and monitors as far as half a mile away have since detected elevated levels of plutonium and americium in the air. Ground and water samples are being analyzed.

Officials said they're confident the incidents are unrelated. And while they emphasize that the levels detected off-site are no more harmful than a dental X-ray, they have not been able to go underground, and have not directly answered questions about how contaminated the tunnels might be.

``There's a whole lot of stuff that we don't know,'' said Hancock. ``A lot more sampling that needs to be done. Then there is going to have to be public discussion about what needs to be done.''

WIPP is the nation's only deep underground geological repository. And opponents will certainly use the case to fight against any expansion of WIPP's mission, which is to take only transuranic waste from federal nuclear sites.

``I'd say the push for expansion is part of the declining safety culture that has resulted in the fire and the radiation release,'' Hancock said.

``I've been talking to (DOE Carlsbad filed office manager) Joe Franco and other people for a while about my concern that we all can get a little complacent when we think we know what we're doing and everything is just fine. ... Distracted nuclear waste disposal is a bad thing because bad things are going to happen.''

Sharif said Hancock's assertions that safety was lax are ``absolutely not true.'''

He said he believes the accidents ``will demonstrate how robust the facility is,'' and that the lessons learned will make it safer.

Carlsbad Mayor Dale Janway concedes, however, the accident could have long-term effects.

``I am worried about the impact,'' he said. ``I'm not worried about the (radiation) levels,

And even after the leak, the project, which employs about 650 people, has strong support in this blue-collar mining town of about 30,000.

``It is important not only for the community, but it's also extraordinarily important for the country,'' said John Heaton, a former state senator and chairman of the Carlsbad Nuclear Task Force. ``Being able to clean up the complex is important for all of us. It is a defense program. All of us in the country have an obligation to deal with the defense issues, whether it's clean up, whether it's fighting wars or preparing for fighting wars.''